If there's a magical way to work out, interval training is it. It's adaptable to all levels and exceptionally useful for losing fat, improving insulin usage, boosting performance and gaining strength. Best of all, it doesn't require hours and hours of dedication to training every day.
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The concept of interval training, is simple: Switch back and forth between bursts of harder and easier exercise (or intense exercise and rest). Athletes have used it for years to improve their endurance. Bodybuilders use it almost exclusively during a cutting phase before competition. And you can use it to look good in your skinny jeans in less time.
Interval Training Takes Many Forms
You may be familiar with HIIT, or high-intensity interval training, which has gained popularity in recent years and involves brief bouts of effort right at your VO2 max followed by an easier, often longer, rest interval. VO2 max is the measure of oxygen you can use during an exercise. So you're pushing yourself right up to your limit.
But, interval training can also be performed aerobically. You boost your effort into a higher, but not maximal, heart rate zone for several minutes and then take it easier for several minutes. Aerobic intervals are great for beginners.
For example, if you’re just starting a running routine, perform short three- to five-minute intervals of a run alternated with three to five minutes of walking to build your stamina. A lot of running newbies use this run-walk method to train for their first race.
A step above HIIT is supramaximal interval training. You perform short bursts of work at a level above your VO2 max alternated with almost complete rest. Tabata routines are a popular example of supramaximal interval training.
Dr. Izumi Tabata researched this format that involves going at more than 100 percent of your effort for 20 seconds, followed by 10 seconds of rest. You repeat it for eight rounds to total four minutes. His research revealed that participants’ aerobic and anaerobic systems improved as a result.
Shorter Training Time With Equal Results
But because you're putting forth so much effort during these work intervals, most interval protocols are notoriously short. You can gain benefits in just 10 to 30 minutes of intervals. Compare this to doing 60 minutes (or more) of steady-state work at a constant, low level. For the busiest of us that still want to fit in a workout, the choice is pretty obvious.
If you do HIIT or supramaximal intervals, aim for no more than sessions per week on nonconsecutive days, as this protocol is pretty taxing on your system. You can still do aerobic intervals or steady-state cardio on the other days to burn calories and stay fit, too.
Read more: Interval Training and Nutrition
Increased Fat-Burning Mechanisms
HIIT and supramaximal intervals are as effective at reducing fat as long bouts of moderate-intensity, continuous cardio, found research published in a 2017 issue of the Journal of Diabetes Research.
Previous research shows that HIIT may be even more effective at turning on specific fat-burning mechanisms. In a study published in a 2008 issue of the International Journal of Obesity, women who underwent 15 weeks of HIIT training lost a significant amount more total body mass, overall fat mass and stomach fat compared to women who did steady state exercise for the same frequency and period of time.
The reasons why high intensity intervals may work better at reducing both subcutaneous fat — fat under the skin — and visceral fat — excess intra-abdominal fat — has to do with increased post-exercise fat oxidation and decreased post-exercise appetite.
Whatever the exact mechanism, multiple studies have demonstrated the benefits of HIIT on fat loss, according to a review of the research published in a 2011 issue of the Journal of Obesity.
Improved Insulin Usage
High-intensity intervals also greatly improve exercisers' fasting insulin levels and their insulin resistance. If you have high fasting insulin levels, it suggests you may suffer from insulin resistance, prediabetes or even early stage type 2 diabetes. Researchers aren't certain why HIIT is so effective in improving insulin sensitivity, but know that it offers numerous benefits.
If you have low insulin sensitivity, you need more insulin — either from your own pancreas or from injections — to keep your blood sugar levels from spiking. You're resistant to the hormone, which indicates your body isn't so good at metabolizing sugar, or glucose.
If your blood sugar levels are too high, as happens in type 2 diabetes, you're susceptible to numerous health problems, including heart disease, peripheral neuropathy and kidney disease.
Interval training is adaptable to just about every fitness level. Beginners can aerobic intervals on a stationary bicycle by alternating a 10 to 20 seconds of pedaling at an intense rate with 30 to 60 seconds of easy revolutions to obtain the health benefits. Elite athletes might do 100-meter all-out sprints alternated with 200 meters at an easy jog to enhance performance.
Intervals, especially HIIT sessions, included as part of an overall workout program can significantly enhance muscle efficiency, as shown in a study published in Physiological Reports in 2017. After six weeks, both older and younger adults experienced improved muscular mechanical efficiency on a cycle egometer having performed three sessions of HIIT per week.
Another study in the Journal of Strength and Conditioning Research published in 2017 showed that sprint-distance triathletes who trained with HIIT for their running workouts while maintaining consistent cycling and swimming workouts improved their overall performance during sprint-distance races.
The researchers concluded that their improvements may be due to enhanced neuromuscular adaptations that occurred during the HIIT workouts, resulting in greatly improved muscle power and work economy.
Read more: 5 Myths About HIIT Debunked